Nuclear membranes of cardiac muscle cells were studied in 134 patients with cardiac hypertrophy of various causes. Abnormalities observed consisted of: 1) increased foldings and convolutions; 2) nuclear pseudoinclusions formed by ctyoplasmic organelles protruding into saccular invaginations of the nuclear membranes, and 3) intranuclear tubules. Some of the intranuclear tubules were straight and cylindrical, and were associated with a peripheral layer of marginated chromatin; others were not associated with chromatin, appeared coiled and followed irregular courses.